The present invention relates generally to the modulation of a signal from one frequency band to another frequency band by multiplying such signal by another signal with a simple wave form which is generally sinusoidal or square.
Modulators have previously been implemented using various types of non-linear devices, such as vacuum tubes, diodes, transistors and switches in combination with either transformers or amplifiers. A typical modulator has been disclosed in U.S. Pat. No. 3,937,882 (Bingham) issued Feb. 10, 1976. Should the design application require that all spurious outputs of a modulator be suppressed to a very low level, individual adjustment of circuit parameters generally has been necessary.
It is often very desirable that electronic network transfer functions be realized using only those components which can be fabricated in large scale integrated circuits. One set of such components comprises switches, capacitors and operational amplifiers. The technology for using these components has become known as switched-capacitor technology and has been described by Hosticka and others in the IEEE Journal of Solid State Circuits, December 1977, page 600.
The transfer functions of switched-capacitor circuits have been shown to be sensitive to the stray capacitances from each plate of the capacitor to the common ground, usually the substrate. The larger of the stray capacitances occurs between the bottom plate of the capacitor and the grounded substrate. However, this stray capacitance can generally be rendered harmless by configuring the circuits so that the bottom plate of the capacitor is connected to the grounded substrate. This configuration will still exhibit circuit sensitivity to the smaller of the stray capacitances occurring between the top plate of the capacitor and the grounded substrate.
Two implementations of switched-capacitor integrators, which are completely insensitive to both of the aforementioned stray capacitances, have been described by Martin and Sedra in Electronics Letters, June 21, 1979, page 365. A complementary pair of inverting and non-inverting integrators was disclosed therein, as well as circuit implementations for various filter sections.